1. Field of the Invention
The present invention relates a method and a system for printing a pair of images on opposite sides of a sheet of recording material on the basis of electronic signal, wherein the recording material is to be put in a paper supply section of a printer by hand to print the image on either side of the sheet. The present invention relates more particularly to a method and a system for preventing the images from being misplaced or misprinted on the sheet.
2. Background Arts
It is well-known to print a pair of images on opposite sides of a sheet of recording paper by feeding the recording sheet twice to a printer. That is, after printing one image on one side of the recording paper, the recording paper is fed to the printer in a reversed or inverted posture for printing the other image on the other side of the recording paper. Some conventional printers are provided with mechanisms for automatically turning over the recording paper to reverse the printing side, called a convertible perfector type. But such a mechanism inevitably enlarges the printer, complicates the printer's construction and results in raising the cost of the printer.
On the other hand, where the printer does not have the automatic paper reversing mechanism, the recording paper having a first image printed on one side thereof has to be manually placed in a paper supply section of the printer again, but in a reversed posture for printing a second image on the other side. If the operator places the recording paper in a wrong posture at that time, the second image would be printed in a wrong direction, e.g. in the upside down posture. If the operator fails to turn over the recording paper, the second image would be printed on the same side as the first image (double-printing).
In order to prevent double-printing, it is known to provide a sensor for checking whether there is any image on the side to print now. However, this solution cannot prevent the second image from being printed in the wrong direction.
It has also been suggested to display an illustration instructing the correct posture of the recording paper after an image is printed on one side of the recording paper. However, if the operator neglects or overlooks the illustration, misplacement of the recording paper or misprinting of the second image cannot be prevented.